The present invention relates to a method for making improved means for opening flexible containers. In particular it relates to a method for incorporating a separate film or membrane having means for tearing and interlocking zipper elements into a bag-like structure to form an easy-open reclosable flexible container. The present invention further relates both to the membrane and flexible containers produced by the method.
Because reclosable flexible containers are by their very nature accessible, accidental or intentional contamination of contents has long been an object of concern. One approach has been to hermetically seal reclosable flexible containers to protect the contents thereof. Use of hermetic seals, however, has required the further development of easy-open features, such as tear strips and perforated or weakened lines for tearing to disrupt the seal and gain access to the bag contents. Many easy-open features desirably evidence any tampering with the container seals.
Among the approaches to hermetically sealing flexible containers is the attachment of separate films or membranes over the mouth opening of a bag-like structure so that the membrane serves as the top edge of a container. See, for example, U.S. Pat. No. 4,874,257 to Inagaki. Thereafter, the membrane which forms the hermetic seal may be ruptured to gain entry to the bag contents, irreversibly evidencing such entry. In Inagaki cutting is evidently the means of rupturing since no other opening means are disclosed.
However, other opening means for rupturing hermetically sealed containers are known. Thus, Siegel, U.S. Pat. No. 4,615,045 discloses a bag structure having a removable bag top closure including interlocking profiles. One flange of the top closure has an upward extension for hanging the bag. Opposing pull flanges form a tongue which seals the bag mouth and may be removed by tearing across serrations, perforations, or weakened lines therein, to gain access to the bag contents. Unless the tongue on the bag is intact, there would be an indication that access to the bag was attained or attempted.
Likewise, Thompson et al in U.S. Pat. No. 4,966,470 discloses various means for rupturing hermetically sealed containers so as to provide a visual, tamper-evident feature on reclosable packages which also include an inner hermetic peel seal and an outer reclosable seal.
Ausnit, U.S. Pat. No. 4,894,975 (the '975 patent), discloses a membrane having interlocking zipper elements. The membrane is folded and sealed to opposing bag walls to form a tamper-evident security seal across the mouth of the bag which also serves as the top edge of the container. The top of the seal may be torn off along parallel lines of weakened tear resistance to open the bag.
Of further relevance is Ausnit et al, U.S. Pat. No. 4,812,074 (the '074 patent), wherein a film containing interlocking zipper elements is sealed to a web of thermoplastic material forming a two-layered area of film and web. Folding the web brings the zipper elements into opposing relationship with the film layer inside and the web layer outside the top edge of the container which results. The film, thus, does not serve alone to seal the edge of the container. The '074 patent further discloses a tear strip located in the film by which both the film and web are torn to gain access to the bag contents.
Problems have arisen in the use of various means to open hermetically sealed containers. Because of concerns with contamination and freshness, use of perforations or serrations to define a weakened line for tearing, as disclosed by Siegel, are not practical in many applications, particularly in packaging foodstuffs. They provide a series of small openings to the bag contents through which bacteria may migrate or contaminants may be introduced undetected. Problems have also arisen with containers having narrowed regions for tear lines as disclosed in the Ausnit '975 patent. For example, consumers have been unable to actually tear the thermoplastic material. Further, once weakened regions are initially torn, irregular tearing may deviate off-line down the bag lips. Irregular tearing is a problem which also accompanies the use of tear strips, such as used in the '074 patent, as the tear lines may deviate down the bag lips and propagate into the zipper elements, compromising the strength, shape and operation of the zipper elements.
Accordingly, further developments are needed to facilitate easy-opening of reclosable containers, while maintaining a tamper-evident barrier to contamination.